1. Field of the Invention
The present invention relates to a method of forming a semiconductor thin film suitable for manufacturing a TFT (Thin Film Transistor) substrate used for a liquid crystal display or an organic EL (electroluminescence) display and an inspection device of such a semiconductor thin film.
2. Description of the Related Art
In an active matrix type liquid crystal display or an organic EL display using an organic EL device, a TFT substrate is used. In the TFT substrate, an amorphous semiconductor thin film or a polycrystalline semiconductor thin film with a relatively small grain diameter is formed on a substrate, and the semiconductor thin film is irradiated with a laser beam and annealed to obtain a crystal grown semiconductor thin film. The obtained semiconductor thin film is used to form a TFT as a drive element.
As a light source of an annealing device by a laser beam as above, in the past, excimer laser that has a high absorption rate of the semiconductor thin film and is capable of obtaining high pulsed light output has been used. However, since the excimer laser is gas laser, the output intensity varies according to every pulse. Thus, there is a disadvantage that in the TFT formed by using the excimer laser, the characteristics vary, and in a display unit using such a TFT, display irregularity is easily generated.
Therefore, for the purpose of resolving image quality deterioration due to the pulse intensity variation in gas laser, an annealing device using semiconductor laser with high output stability as a light source has been proposed (for example, Japanese Unexamined Patent Application Publication No. 2003-332235). However, since the light output obtained from the semiconductor laser is extremely small compared to that of the excimer laser or the like, the beam size in annealing treatment is also decreased. Therefore, annealing treatment time per unit area of the TFT substrate is increased, leading to disadvantages such as lowering of productivity and increase of manufacturing cost.
As a result, for the purpose of realizing a high throughput of annealing treatment, the following annealing method has been proposed (for example, Japanese Unexamined Patent Application Publication No. 2004-153150). In the annealing method, a plurality of laser light sources are arranged close to each other, and a plurality of regions on an amorphous semiconductor thin film are concurrently irradiated with a plurality of laser beams from the plurality of laser light sources. As a result, scanning time is reduced to increase productivity.
Meanwhile, in the past, a method of controlling crystallization of the semiconductor thin film using the semiconductor laser as above has been performed by a means for monitoring a laser beam intensity provided for the annealing device. For example, in the method of monitoring a laser beam intensity described in Japanese Unexamined Patent Application Publication No. 2005-101202, a single intensity measurement section is used for light paths of a plurality of laser optical systems. The single intensity measurement section is moved onto each light path of each laser optical system to allow the single intensity measurement section to receive light in each light path. Thereby, for the plurality of laser optical systems, each irradiation energy is measured by the single intensity measurement section.
Further, in Japanese Unexamined Patent Application Publication No. 2004-342875, a method of analyzing a laser irradiation position by using Raman scattering light emitted from crystal by irradiation of a laser beam is proposed. In addition, a defect inspection method and a device thereof using a reflection image of a high speed line camera have been proposed.